Attempt to use an in vitro assay to study the events which eventually lead to destruction of tumor cells by activated macrophages: by determining if sensitized lymphocytes stimulated with tumor antigen generate macrophage activating factor (MAF) or factors capable of enhancing macrophage mediated cytotoxicity; by further defining the nature of the interaction between MAF and macrophages which results in enhancement of the cytotoxic capacity of activated cells; and by exploring the mechanisms by which macrophages, once activated, kill tumor cells.